>
> Just out of interest, Unicode has the combining marks U+030D and U+030E for
> Marshallese, so I presume the language has been considered. Is the vowel &
> unified with U+0026 AMPERSAND?

Yes. Since that is how it is typed and typeset.

> The latter isn't a letter of course...

Not in most languages, but in Marshallese, it is. This is the price one
pays for adopting a non-letter as a letter of your alphabet. Mayan
orthographies that used "7" for glottal stop have a similar problem.